The New Zealand Society of Genealogists (NZSG): www.genealogy.org.nz is a reputable and quality organization which you should never hesitate to contact for your research needs. The question is why would a non-New Zealand genealogists need their help?
I’m a firm believer that in order to reconstruct the entire story of a family, you have to trace out the siblings of your ancestor no matter where they immigrated. That’s one approach. Another approach is that it may be within the New Zealand branch of the family that the birthplace in Ireland for the entire family is preserved. Birthplaces are often difficult to identify from North American and UK records. However, they are more common place in New Zealand records.
NZSG has an active Irish Interest Group: www.genealogy.org.nz/Irish_Interest_Group_202.aspx and to perhaps broaden your horizons a Maori Interest Group: www.genealogy.org.nz/Maori_Interest_Group_205.aspx Since the Irish definitely intermarried with this ethnic group, Maori Studies should never be neglected in your explorations. In 2011, the Irish Interest Group library holdings were integrated into the NZSG collection. The combined collection resulted in one of the best material collections of Irish resources in New Zealand
The Society publishes the bi-monthly journal The New Zealand Genealogist which is a
respected journal in family history. They have also been active in indexing records, and producing CDs. The current “Kiwi Index v. 1.0” CD has over 8 million entries from a variety of sources. NZSG members have access to this CD. A list of sources on the CD can be found on the website.
Whether you have an ancestor or a branch of your family who settled in New Zealand, then you will benefit from learning more about the resources at the NZSG. Remember, the answer to Irish origins may lie in a New Zealand record!